1. Field of the Invention
The invention relates to the art of engraving a surface, often for the purpose of providing a decorative design on a previously hardened concrete, asphalt or other workable surface.
2. Background Information
Many earlier inventors have taught methods of concrete decoration in which a stencil is laid on a concrete surface and wet, colored concrete materials are added to the pre-existing surface through holes in the stencil. Notable among teachings in this area are the following patents:
U.S. Pat. No. 5,792,511, wherein Oliver et al. show a stencil that remains embedded in the decorative coating. PA1 U.S. Pat. No. 5,735,094, wherein Zember describes a coating process using specific materials and involving pulling a stencil out of the coating before it sets up. PA1 U.S. Pat. No. 5,447,752, wherein Cobb describes a similar process using different materials. PA1 U.S. Pat. No. 5,243,905, wherein Webber teaches a stencil comprising interlocking segments and used in a coating process. PA1 U.S. Pat. No. 5,133,621, wherein Gonzales describes a way of putting isolated decorative figures in a wet concrete slab. PA1 U.S. Pat. No. 5,038,714, Dye et al. teach an arrangement for spraying a dye, but not additional concrete, through a stencil having a gasket on the bottom thereof.
The inventor, in his U.S. Pat. No. 5,176,426 and U.S. Pat. No. 5,445,437, has taught method and apparatus for engraving decorative figures into a hardened concrete surface by guiding a cutting apparatus across the surface to be decorated. These arrangements have generally employed small wheeled carts carrying abrasive grinding wheels.
Apparatus of the sort generally referred to as "flux chippers" or "needle scalers" is also of interest. In these sorts of apparatus one or more impacting tools, retained for translational motion of a limited extent along a predetermined axis, are repeatedly driven into the surface to be engraved by impacts from a hammer that is conventionally pneumatically operated, but that could be electrically or hydraulically driven. A needle scaler typically uses ten to thirty pointed rods, called "needles", as the impacting tools. Each of these needles may have a diameter of two to three millimeters and commonly has a nail-head end distal from the pointed or beveled work-impacting end that commonly projects outwardly from a nosepiece of the apparatus. A pneumatically driven hammer head strikes the array of needles and is returned to the beginning of its reciprocating stroke by a return spring. This arrangement provides several thousand blows per minute on the array of nail heads and thereby repeatedly drives the needles back and forth over a total stroke distance of some three centimeters. Needle scalers are generally used in a freehand mode and are made with a variety of grips and nose configuration to adapt them to differing applications. The uses for needle scalers include cleaning rust (e.g., mill scale) from iron and steel castings, peening welded joints, removing barnacles from marine apparatus, and chipping stone, concrete and brick.
In addition to the use of grinding wheels and of chisels, it is also known to engrave hard surfaces by sandblasting, shot peening and other such techniques in which impacting tools, comprising small particles of a hard material, are expelled from the nose or nozzle of a tool driving or dispensing means and energetically impact a surface being engraved. When used to make deep cuts in hardened concrete or other aggregate materials comprising segregated portions of differing hardness, sandblasting leads to an engraved region having a rough texture because the softer portions of the concrete are removed more easily than harder ones.